A capacitor with exceptionally large capacitance - and therefore energy storage - for its size and weight. That means one hundred to one thousand times more than even an electrolytic capacitor. Supercapacitors are sometimes defined more narrowly as electrochemical double layer capacitors. These are made from carbon aerogel, carbon nanotubes, or highly porous electrode materials and have extremely high capacity. They can be used in some applications instead of rechargeable batteries or to enhance their performance. Other forms of supercapacitor have been proposed but not validated.